Chip mounting with flowable layer

ABSTRACT

A circuit structure may be formed in a substrate having a face and an open trench, where one or more chips are to be mounted. At least one bridge may extend across an intermediate portion of the trench, and optionally, may divide the trench into sections. A conductive adhesive layer may be applied to the substrate face and, if included, the bridge. One or more circuit chips may be mounted on the adhesive layer, with at least one edge of one circuit chip adjacent to the trench. Alternatively or additionally, an adhesive layer may be applied to a base of a chip and then mounted to the substrate face, in like fashion. The trench may accommodate excess adhesive flowing out from under the one or more chips, while the bridge retains the adhesive across the width of the trench. If the adhesive is conductive, this provides continuity of the conductive layer on the face of the substrate across the trench. In one example, pairs of circuit chips may be effectively mounted in adjacent relationship for interconnection without interference from excess adhesive.

RELATED APPLICATIONS

This application is a division of application Ser. No. 10/883,356, filedJun. 30, 2004, which application is incorporated herein by reference inits entirety for all purposes.

BACKGROUND

Some circuits for use at communication frequencies, such as are used fortelecommunication and other signal processing applications, involvemounting one component onto another component. An example is mounting anintegrated circuit chip to a base substrate. Various mounting techniquesmay be used. One technique involves using an adhesive to attach or“bond” a chip to a substrate. During this process, adhesive may besqueezed from between the chip and substrate and flow to regions beyondthe chip footprint. If the bonding involves two chips or a chip beingbonded near another above-the-substrate structure, a likely result is anoverflow of adhesive onto contact pads required to interconnect the chipand another circuit component.

BRIEF SUMMARY OF THE DISCLOSURE

A circuit structure may be formed that includes a substrate having aface and an open trench, adjacent to where one or more chips are to bemounted. One or more bridges may extend across an intermediate portionof the trench, and optionally, bifurcates or otherwise divides thetrench into sections. An adhesive layer, that may or may not beconductive, may be applied to the substrate face. One or more circuitchips may be mounted on the adhesive layer, with at least one edge ofone circuit chip adjacent to the trench. Optionally, an adhesive layermay be applied to the chip base and then mounted to the substrate face,in like fashion. The trench may accommodate excess adhesive. A bridgeacross the trench may retain the adhesive across the width of thetrench. This may extend the adhesive surface area, and when the adhesiveis conductive, the bridge may provide continuity of the conductive layeracross the face of the substrate. In one example, pairs of circuit chipsmay be effectively mounted in adjacent relationship for interconnectionwithout interference from excess adhesive by positioning adjacent edgesof the chips adjacent the trench.

BRIEF DESCRIPTION OF THE SEVERAL FIGURES

FIG. 1 shows an isometric view of a pair of chips on top of a bridgedtrench.

FIG. 2 shows a plan view of interconnected chips mounted on a substrate.

FIGS. 3A and 3B show initial assembly process steps.

FIG. 3C shows a cross-sectional view of FIG. 2 taken along line 3-3, asa final process step.

FIG. 4 shows a cross-sectional view of FIG. 2 taken along line 4-4.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

Referring to the drawings, FIGS. 1, 2, 3C and 4 show a circuit structureincluding a base substrate 12 on which are mounted one or more circuitunits 14, such as circuit chips 16 and 18. Substrate 12 may be anysuitable substrate for supporting circuit units 14. For example, thesubstrate may be made of one or a combination of dielectric,semiconductive, and conductive materials. Also, the substrate may or maynot be printed with one or more circuit elements that are active and/orpassive, whether or not any such circuit elements are or are not in acircuit including circuit units 14. Circuit units 14, including circuitchips 16 and 18, may be any suitable active or passive circuit devices,such as, but not limited to, resistors, capacitors, inductors,transmission lines, diodes, and transistors, or a combination of suchdevices. Accordingly, the circuit chips may include passive and/oractive circuit devices, and may be formed on a chip substrate that maybe a dielectric, semiconductive or conductive material, or a combinationof such materials. A representative example of a chip may include anintegrated circuit chip, such as a monolithic microwave integratedcircuit (MMIC) or an application specific integrated circuit (ASIC).

As particularly shown in FIGS. 3C and 4, substrate 12 may include aprimary face 12 a on which an adhesive layer 20 may be placed forholding circuit chips 16 and 18 on the substrate. A trench 22 extendsalong a length of substrate 12, and may include two or more trenchsections 24 and 26. Trench sections 24 and 26 may also be considered tobe separate trenches, so the term trench, as used herein, includes oneor more separate trenches, whether connected or disconnected, andwhether aligned or misaligned. Trench sections 24 and 26 may havesidewalls, such as sidewalls 24 a, 24 b and 26 a, 26 b. These sidewallsmay define the sides and lengths of the trench sections. The trench mayextend beyond the edges of the circuit chips 16 and 18, as shown, orthey may end along the circuit chips, such as optional trench end 24 cnear the outer edge of the chip circuits, as shown in FIG. 4.

One or more bridges, such as bridge 28, may extend across trench 22. Insome examples of the circuit structure, there is no bridge 28. In otherexamples a plurality of bridges 28 may be used, as represented byadditional or alternative bridges 28 shown in dashed lines. Any bridgeor bridges may be formed during the formation of trench 22. For example,the trenches may be formed by etching, such as with a laser, substrate12. By etching discontinuous trench sections, a stretch of substrateremaining may form the bridge. In such a case, the bridge may be a wallbetween trench sections or the substrate between the ends of twotrenches. The bridge may also extend over or through an intermediateportion of a continuous trench, leaving a passageway along the trenchand under the bridge. Further, a bridge 28 could be grown or insertedinto a previously formed trench, as an alternative to leaving a portionnon-etched. Thus, the term bridge refers to any suitable structurespanning a width of the trench sufficient to support adhesive layer 20.In some examples, such as circuit structure 10 as shown, the adhesivelayer is conductive, and the bridge supports a continuous adhesive layer20, providing electrical continuity between opposite sides of thetrench. The layer support may preferably be provided, by a bridge withan upper surface 28 a near substrate surface 12 a.

In this example, circuit chips 16 and 18 have respective connection orlead pads, also referred to as terminals 30 and 32 that may be connectedto resident circuit structure formed on or in the chips. This residentcircuit structure may be connected to external circuit structure viaterminals, such as terminals 30 and 32. In this example, an interconnect34 interconnects terminals 30 and 32. Any device suitable for providingan electrical connection between the terminals, such as a wire, ribbonor bar, may be used. In this example, interconnect 34 is in the form ofa bond wire 36 attached, such as by solder, to the terminals.

One or more circuit units may be positioned adjacent to a trench. Thearea near a portion of a circuit unit that is adjacent to a trench isreferred to as an area 38 of adjacency. The figures show an example inwhich two circuit units 14 are positioned adjacent to a trench 22. Thespace between two circuit units may also be referred to as a gap 40. Allor a portion of gap 40 may extend over trench 22. Gap 40 may bepositioned completely or partially over trench 22 so that excessadhesive flows directly into the trench. Centering the gap over trench22, as shown in FIG. 2, is not required, as the trench may be offsetfrom the gap, and the gap may be wider than, the same width as, ornarrower than the trench.

FIGS. 3A-3C illustrate steps of one example of a method of bonding acircuit unit onto a substrate. Initially, a base substrate 12 isselected. Trench 22 may be formed prior or subsequent to the placementof one or more circuit units on the substrate. In this example, as shownin FIG. 3A, trench 22 and bridge 28 are formed in substrate 12. Anadhesive layer 20 is then laid down on top of substrate 12, as shown inFIG. 3B. Chips 16 and 18 are mounted side-by-side, as shown in FIG. 3C,which shows a cross-sectional view from the side of the mounted circuitchips. Terminals 30 and 32, positioned near the adjacent respectiveedges of chips 16 and 18, are interconnected using wire bond 34.Although interconnection of chips 16 and 18 may occur after mounting thechips on the adhesive layer, the chips may be interconnected prior to orduring mounting of the chips.

Adhesive layer 20 may be conductive to provide a circuit ground circuitstructure 10, including circuit chips 16 and 18. Adhesive 20 may beflowable, and may squeeze out from under one or both of the chips duringmounting. Such excess adhesive may flow into the trench, rather thanfurther out onto the substrate surface 12 a. In this example, gap 40between the chips may be small. The adhesive may thereby flow into thetrench rather than up between the chips, and possibly on top of thechips, where it might flow onto terminal 30 or 32. In this way, theterminals may remain clear of adhesive, and interconnection may occurunimpeded by uncontrolled flow of adhesive.

Further, with a conductive adhesive, ground or circuit continuity ismaintained, regardless of how much adhesive flows in trench 22. Ifbridge 28 is wide enough, adhesive may still accumulate on top of it,even to the point of overflowing onto the top of one or both of thechips.

More than one bridge 28 may be used to create a greater assurance ofcircuit continuity between chips 16 and 18, especially where conductiveadhesive 20 may be less viscous. Also, trench 22 need not extend deeperinto substrate 12 than is needed to accommodate enough adhesive to avoidbuild-up on top of a circuit chip. However, a trench 22 may be formedthat is sufficiently deep to accommodate a range of amounts of excessadhesive.

Now referring to FIGS. 3C and 4, when chip 16 is mounted adjacent tochip 18 (or to some other above-the-substrate circuit unit) on substrate12 using conductive adhesive 20, and in preparation for beingelectrically connected, an edge of at least one chip (16 or 18) may beplaced adjacent bridge 28. Therefore, trench 22 receives any excessadhesive 20 during bonding, and bridge 28 allows adhesive 20 to remaincontinuous across the trench despite that some adhesive 20 drops intothe trench. The continuity of adhesive 20 from the underside of eachchip 16 and 18 to the space between the chips along bridge 28 is readilyapparent in FIG. 3 and generally required to retain continuity of groundbetween chips 16 and 18. Depending on the viscosity of the adhesivelayer, each bridge 28 may be formed with a width less than twice theheight of an adjacent circuit chip or a height of the shortest chip.Adhesive may flow off of the sides of the bridge into the trench as wellas directly from the chip into the trench. The likelihood that therewill be a build-up of adhesive on the bridge above the height of a chipis reduced if the bridge width is less than or equal to the height ofthe shorter of the chips. Although the bridge may be positioned to theside of the chips, as shown in phantom lines in FIG. 2, it may also bepositioned under interconnect 34. When in this latter position, adhesiveground layer 20 is directly under the interconnect, and theelectromagnetic field between the interconnect and ground is relativelystrong and well defined.

In another configuration (not shown), trench 22 may extended well beyondthe sides of a circuit chip so as to accommodate the placement ofadditional circuit chips along the same trench. Thus, forming a mask foretching the trench may be simplified and a higher density of circuitunits may be realized.

Accordingly, while embodiments have been particularly shown anddescribed with reference to the foregoing disclosure, many variationsmay be made therein. The foregoing embodiments are illustrative, and nosingle feature or element is essential to all possible combinations thatmay be used in a particular application. Where the claims recite “a” or“a first” element or the equivalent thereof, such claims include one ormore such elements, neither requiring nor excluding two or more suchelements. Further, ordinal indicators, such as first, second or third,for identified elements are used to distinguish between the elements,and do not indicate or imply a required or limited number of suchelements, and do not indicate a particular position or order of suchelements unless otherwise specifically stated.

It is believed that the following claims particularly point out certaincombinations and subcombinations that correspond to disclosed examplesand are novel and non-obvious. Other combinations and subcombinations offeatures, functions, elements and/or properties may be claimed throughamendment of the present claims or presentation of new claims in this ora related application. Such amended or new claims, whether they aredirected to different combinations or directed to the same combinations,whether different, broader, narrower or equal in scope to the originalclaims, are also regarded as included within the subject matter of thepresent disclosure.

INDUSTRIAL APPLICABILITY

The methods and apparatus described herein are applicable to thesemiconductor, the telecommunication, and the communication-frequencysignal processing industries, and are applicable to circuit technologieswhere circuit units may be mounted on a substrate.

1. A method comprising: forming a trench in a substrate having a face;covering the substrate face with a flowable conductive layer; andmounting at least a first circuit chip on the conductive layer with anedge adjacent to the trench in a manner causing a portion of theconductive layer to flow into the trench.
 2. The method of claim 1,further comprising mounting a second circuit chip on the conductivelayer adjacent the first circuit chip.
 3. The method of claim 2, wherethe first and second chips each have at least one terminal, and furthercomprising interconnecting the one terminals of the first and secondcircuit chips.
 4. The method of claim 2, of which forming a trenchincludes forming at least one bridge spanning an intermediate portion ofthe trench.
 5. The method of claim 4, of which forming the at least onebridge includes forming the at least one bridge with a width less thantwice a height of one of the circuit chips.
 6. The method of claim 5, ofwhich forming the at least one bridge further includes forming the atleast one bridge with a width that is less than or equal to the heightof the one circuit chip.
 7. The method of claim 2, of which the edge ofat least one of the circuit chips is mounted to extend at leastpartially over the trench.
 8. The method of claim 4, of which formingthe at least one bridge includes dividing the trench into one or moretrench sections.
 9. The method of claim 8, of which dividing the trenchincludes forming at least two separate trench sections, with one of theat least one bridge extending between ends of the trench sections.
 10. Amethod comprising: forming a trench having sidewalls in a substrate;forming at least one bridge between the sidewalls of an intermediateportion of the trench; applying a flowable adhesive to the substrate andbridge; and bonding a pair of circuit chips in adjacent relationship onthe adhesive with an area of adjacency of the chips located generallyover the trench, with excess adhesive flowing into the trench.
 11. Themethod of claim 10, further comprising interconnecting exposed terminalson the chips.
 12. The method of claim 11, of which forming a trenchincludes forming the at least one bridge spanning an intermediateportion of the trench.
 13. The method of claim 12, of which forming theat least one bridge includes forming the at least one bridge with awidth less than twice a height of one of the circuit chips
 14. Themethod of claim 13, of which forming the at least one bridge furtherincludes forming the at least one bridge with a width that is less thanor equal to the height of the one circuit chip.
 15. The method of claim10, of which forming the at least one bridge includes dividing thetrench into separate trench sections.